This invention relates to a method of selectively oxidizing an aluminum-bearing III-V layer in a phosphorous-rich III-V material system. This invention also relates to a product made by such a method.
Selective oxidation of semiconductor materials has been used successfully in designing various novel device structures. For example, oxidation of silicon is very popular in forming microelectronic devices. Recently selective oxidation of III-V semiconductor materials, i.e., a compound semiconductor material with elements from the Group III and Group V column of the Periodic Table, based on aluminum arsenide/gallium arsenide has been demonstrated. Wet thermal oxidation of AlxGa1xe2x88x92xAs layers is gradually being introduced in the optoelectronic device-manufacturing arena as it has proved to be a well controlled repeatable process. However, this oxidation process is limited to high aluminum content III-V based material systems such as AlxGa1xe2x88x92xAs lattice matched to GaAs.
While optical devices grown on this GaAs based material system typically have a wavelength of operation shorter than 1.0 xcexcm (1000 nm), optical telecommunication systems generally operate at a longer wavelength of 1.55 xcexcm. Devices used in the massively deployed base of a telecommunication network are not typically fabricated on a GaAs substrate. Instead, the material system of choice for optical communication systems is lattice matched to Indium Phosphide (InP).
Unfortunately, the only high aluminum content III-V materials that are lattice matched to InP are AlAsxSb(1xe2x88x92x) materials with an x value near 0.5. There is no x value for which AlxGa(1xe2x88x92x)As is lattice matched to InP. AlyIn(1xe2x88x92y)As materials are more suitable but are only lattice matched to InP for y values near 0.48, which has a relatively low aluminum content for selective oxidation purposes. As a result, the advantages of selectively oxidized structures cannot be easily transferred to devices based on InP substrates.
The maximum Al composition of an arsenide-based III-V ternary material that is lattice matched with InP is Al0.48In0.52As. Because of the relatively small Al composition, the oxidation rate in this material has been observed to be very slow (xcx9c1 xcexcm/hour at 500xc2x0 C.). There have been efforts in pseudomorphically growing AlAs layers on InP substrates, but because of the huge lattice mismatch, the strain is detrimental to device performance and reliability.
Recently, strain-compensated ultra short-period InAs/AlAs short period super-lattices (SSLs) have been used for selective oxidation of InP based devices. A super lattice (SL) is a structure with alternating layers of different composition. Each layer of the SL may be quite thin. Generally a SL will have many periods of alternating layers, but the period should be at least two, i.e., the layers should repeat at least once. The layers of an SSL are only a few monolayers (ML) thick. Thus, the period of an SSL is short.
It would be an advantage to provide a method of forming an oxidation layer where the oxidation layer can be readily and efficiently selectively oxidized in a controllable and repeatable way, and where the method is compatible with current optoelectronic device fabrication technologies.
It would be an advantage to provide a method of selectively and rapidly forming an oxide layer in a phosphorous-rich III-V material system in a repeatable and controllable way without necessarily requiring lattice-matching.
According to one embodiment of the invention there is provided a method of selectively oxidizing III-V semiconductor material grown on a substrate within a phosphorous-rich material system comprising the steps of: providing a III-V compound semiconductor system comprising a short-period super lattice (SSL) of N periods of alternating layers of an aluminum-bearing III-V semiconductor material and a second III-V semiconductor material where Nxe2x89xa72, at least one phosphorous-rich III-V semiconductor layer, and at least one substantially phosphorous-free III-V semiconductor layer between each of the at least one phosphorous-rich layers and the SSL; and exposing the III-V semiconductor system to oxidizing atmosphere to selectively oxidize at least a portion of the SSL. A product formed by this method is also provided.
The method may further comprise removing a portion of the SSL to expose the edges of the alternating layers prior to the exposing to oxidizing atmosphere step. The removing step may comprise etching, cleaving, or sawing the III-V semiconductor system.
The at least one phosphorous-rich layer may comprise one of an InP, InGaAsP and GaP layer.
The at least one substantially phosphorous-free layer may comprise a substantially phosphorous-free super lattice (SL). The at least one substantially phosphorous-free SL may comprise a GaAs/InAs SSL. The at least one substantially phosphorous-free SL may be unstrained or strain-compensated to the substrate. The at least one substantially phosphorous-free layer may be an analog of the SSL. The at least one substantially phosphorous-free layer may comprise In0.52AlxGa0.48xe2x88x92xAs, wherein x is much less than 0.48 so that the oxidation rate of the phosphorous-free layer is low. The at least one substantially phosphorous-free layer may be phosphorous-free.
The SSL may be strain compensated. The SSL may have a total thickness in the range of about 20 to about 5000 nm.
The at least one phosphorous-rich layer may comprise an InP substrate. The at least one phosphorous-rich layer may comprise InGaP.
The aluminum-bearing material may comprise In0.52AlxGa0.48xe2x88x92xAs, wherein x is approximately 0.48. The aluminum-bearing material may comprise AlAs. The aluminum-bearing material may comprise AlGaAs.
The second material may comprise InAs.
The III-V semiconductor system may comprise one of a semiconductor laser, a semiconductor optical amplifier, a passive waveguide, a Vertical Cavity Surface Emitting Laser (VCSEL), and an in-plane laser.
The substantially phosphorous-free SL may comprise an InAs/GaAs/AlAs SSL or an InAs/AlAs SSL.
Each of the layers of the aluminum-bearing material may be two to three monolayers (ML) thick. Each of the layers of the second material may be two to three monolayers thick. The second material may be InAs and two to three ML thick. The aluminum-bearing material may be AlAs and two or three ML thick.
The exposing to oxidizing atmosphere step may comprise exposing the III-V semiconductor system to a moist N2 gas flow. The exposing to oxidizing atmosphere step may comprise exposing the III-V semiconductor system to moisture at a temperature of about xe2x89xa7500xc2x0 C. The exposing to oxidizing atmosphere step may comprise exposing the III-V semiconductor system to an oxidizing atmosphere at a temperature of about xe2x89xa7480xc2x0 C. The exposing to oxidizing atmosphere step may comprise exposing the III-V semiconductor system to an oxidizing atmosphere including at least one of ozone, H2/O2, and moisture. The exposing to oxidizing atmosphere step may comprise exposing the III-V semiconductor system to steam at a temperature of about 515xc2x0 C.
The number of periods N may be xe2x89xa750.
The at least one phosphorous-rich III-V semiconductor layer may comprise phosphorous-rich III-V semiconductor layers on both sides of the SSL.
According to another embodiment there is provided a method of selectively oxidizing III-V semiconductor material comprising the steps of: providing a III-V semiconductor system comprising a InAs/AlAs short-period super lattice (SSL) of N periods of alternating layers of AlAs and InAs where Nxe2x89xa72, at least one phosphorous-rich III-V semiconductor layer, and at least one substantially phosphorous-free III-V semiconductor layer between each of the at least one phosphorous-rich layers and the SSL; and exposing the III-V semiconductor system to moisture at a temperature of about xe2x89xa7500xc2x0 C. to selectively oxidize at least a portion of the SSL.
According to another embodiment there is provided a method of selectively oxidizing III-V semiconductor material comprising the steps of: providing a III-V semiconductor system comprising a InAs/AlAs short-period super lattice (SSL) of N periods of alternating layers of AlAs and InAs where Nxe2x89xa72, at least one phosphorous-rich III-V semiconductor layer, and at least one substantially phosphorous-free III-V semiconductor layer between each of the at least one phosphorous-rich layers and the SSL; and exposing the III-V semiconductor system to an oxidizing atmosphere at a temperature of about xe2x89xa7480xc2x0 C. to selectively oxidize at least a portion of the SSL.